1. Field of the Invention
This invention relates to an apparatus for detecting data of an uneven surface, such as human fingerprint and the like, in a personnel identification apparatus. More particularly, this invention relates to an uneven surface data detection apparatus having a thin structure.
2. Description of the Related Art
In today's high-tech world of information, a strong demand has arisen for better computer system security techniques. In particular, to protect confidential data, a reliable identification must be made of personnel in charge of such systems, and thus strict checks upon entrance to a computer room have become very important. In the past, passwords and identification (ID) cards have been used, and now personal identification systems using fingerprints are increasingly used.
In a first conventional method for entering uneven surface data (e.g., a fingerprint), a fingerprint is printed on paper using ink and is then sensed using an image sensor. In this case, however, a finger must be stained with ink each time the fingerprint data is to be entered, and any uneven coating or blurring of the ink greatly hinders the input operation.
In a second conventional method, a light beam is incident on a glass/air interface at a critical angle or larger, and thus an uneven surface pattern is instantaneously obtained. In this method, such as seen from FIG. 21, an uneven surface data detection apparatus uses a prism 2, a finger surface (uneven surface) pattern of a finger 1 having projections (ridges) 6 and recesses (grooves) 5 is pressed against an oblique side portion of the prism 2, and light from a light source 3 is made incident on an oblique side portion thereof at a critical angle or larger. The incident light is scattered by the projections 6 and is totally reflected by the glass/air interface in the recesses 5, and is then incident on a detector (e.g., an imaging element) 4, to thereby detect the uneven surface pattern. Nevertheless, light leaks through an unclean oblique surface caused by remaining fingerprints or moisture, and this leakage light irradiates the recessed portions 5 of the fingerprint and is scattered. Therefore, the level of the signal light from the projected portions 6 is lowered, and thus the contrast of the uneven surface pattern is also lowered. Further, since a prism is used, the total thickness of the apparatus cannot be reduced.
In a third known method, such as seen from FIG. 22 (and disclosed such as in U.S. Pat. No. 4,728,186), the apparatus includes a transparent body 7 made of glass or plastic and having a lower surface 7-1 and an upper surface 7-2 parallel to each other, and a diffraction grading 8 including a lens. A finger surface (uneven surface) pattern of a finger is pressed against one of the surfaces, i.e., the upper surface 7-2, and light is irradiated from the lower surface 7-1 in a direction substantially perpendicular to the transparent body 7. Air layers exist in the recess 5 of the finger, so that the light which enters the recess 5 is reflected at positions on the surface of the recess 5 and scattered in random directions. Most of the light again enters the transparent base 7 is discharged from the other surface 7-1, at the same angle as the light enters to the base 7. On the other hand, the light which reaches the convex 6 is scattered into the transparent base 7, so that a part of the light is discharged from the transparent base 7 as shown at R2, and the remaining is totally reflected and transmitted through the transparent base 7 as shown at R3. The light R3 is derived from the diffraction grading 8 and enters to an image sensor 4, such as a CCD, in which an image of the fingerprint can be obtained.
In the known fingerprint detection apparatus as shown in FIGS. 21 and 22, the optical elements, such as an image sensor, a diffraction grating, or the like, must be located opposite to and spaced from the fingerprint contact surface, and therefore, a relatively large space is required for obtaining the image data of the fingerprint. That is, an apparatus known in the prior art must have a relatively large thickness, and this makes it difficult to incorporate such a fingerprint detection apparatus in a door, a keyboard of computer terminals or the like.